Low complexity algorithms for speech and audio coding constitute a very relevant asset, for instance for mobile terminal based communications. Due to low storage and low complexity, while preserving coding efficiency, structured codebooks may be preferred in several state of the art speech and audio codecs, like for instance the Enhanced Voice Service (EVS) codec to be standardized within the Third Generation Partnership Project (3GPP).
Most of today's state of the art speech and audio codecs incorporate transform coding into their structure. The transform coefficients form a long vector (hundreds of samples, depending on the sampling frequency) that is encoded with a given bitrate for each frame. The encoding is done by splitting the long vector in subvectors that can be encoded using a variable rate per subvector approach. For low bitrates it is more efficient to select the subvectors that are represented by non null codevectors and to encode separately the position of such vectors.